Large quantities of petroleum exist in the United States and many other parts of the world which are so viscous that they cannot be recovered using systems which are employed for normal petroleum production. These highly viscous reserves of petroleum are often found in sandstone stratas and because of the high viscosity of the petroleum in the sandstones, such formations are commonly referred to as tar sand. The petroleum in the tar sand may vary from extremely viscous liquids to solids.
Much work has been done towards finding means of recovering the petroleum from tar sands operating from the earth's surface. The general technique is to attempt to change the in situ viscosity of the petroleum in the tar sands to the point where it will flow into a well and can be pumped to the earth's surface. Among the types of endeavors to recover petroleum from tar sands include the injection of solvents, the injection of steam or hot water, and heating the petroleum by in situ combustion. All of these techniques have enjoyed some measure of success when the circumstances are right. However, all efforts to date have not been successful in removing substantial quantities of petroleum from tar sands, and therefore, an improved means needs to be devised so that these large reserves of petroleum can be made available.
It is therefore an object of this invention to provide an improved means of recovering viscous petroleum products from an underground strata. More particularly, an object of this invention is to provide a method of recovering petroleum from an underground strata wherein the in situ viscosity of the petroleum prohibits the petroleum from freely flowing to a well for pumping to the earth's surface, the method including mining shafts below the hydrocarbon bearing strata to provide drilling stations wherein a multiplicity of wells may be drilled upwardly into the petroleum bearing strata, and including improved means of changing the viscosity of the petroleum in the strata so that it can be pumped to the earth's surface. Other objects of the invention include: the development of a mined enhanced recovery process using drilled shafts for access; development and operation for removal of petroleum from positions beneath the hydrocarbon bearing strata; providing methods of multiple point injection of viscosity reducing material and withdrawing hydrocarbons having improved viscosity from a single drilling station; a method of gravel packing of injection or producing wells; and a method of injecting viscosity improving agents and production of petroleum from a common well bore.
These objects, as well as other and more specific objects of the invention will be understood from the following description and claims, taken in conjunction with the attached drawings.